Rotary piston engine

ABSTRACT

The present invention relates to a rotary piston engine to be used as a pump or an engine, comprising a housing ( 1 ) fitted with end walls ( 8, 9 ), a rotary body ( 2 ) rotatably mounted in said housing, and at least one sealing element ( 7 ) separating a volume formed between the housing ( 1 ) and the rotary body ( 2 ), said housing having at least one pair of inlet and outlet openings and the sealing element ( 7 ) having two legs portions, the ends of which abut against the rotary body ( 2 ), and a web portion intermediate said leg portions, said sealing element additionally being pivotable about a pivot axis on said web portion. The sealing element is movably associated with the housing in such a manner that the sealing element is displaceable radially, thus allowing the sum of the distances from the axis of rotation of the rotary body to the points of abutment on said body to vary.

TECHNICAL FIELD

The present invention relates to a rotary piston engine to be used as apump or an engine, comprising a rotor part mounted in a housing fittedwith end walls and with at least one inlet and one outlet opening.Between each pair of inlet and outlet openings there is provided asealing element separating the volume formed between the housing and therotor part to prevent transport of medium between the inlet and outletopenings.

BACKGROUND

Owing to their simple construction and simple mode of operation, rotarypiston engines theoretically may be used for a wide range ofapplications. The constructions used so far have been employed mainlyfor such hydraulic-technical applications where oil or otherself-lubricating and non abrasive fluids are transported and the fluidsare free of particles. The reason for this restricted use is that rotarypiston engines, as presently designed, possess properties thatdiscourage conveyance of abrasive materials through the engines since ifthey were, the wear would become too considerable, affecting enginereliability and performance.

The weakest point of these prior-art rotary piston engines is found inthe movable partition wall that separates the suction and pressure sides(in pump applications) from one another. This partition wall usually isdesigned as a movable slide means that abuts against the rotary pistonsurface and by means of a force applied thereon is pressed in thedirection towards the centre axis of the piston to provide a sealingaction.

The pressure is applied by spring means, hydraulic means or in any othermanner. The pressure requirements of the slide means depend on thepressure that has built up inside the engine and on the speed ofrotation as well as on the configuration of the sealing surface (curveline) of the rotary piston.

In these rotary piston engines the slide means is carefully mounted in agroove/seat and moves with narrow tolerances in outwards and an inwardsdirection motion. The construction is sensitive to wear and othermechanical influences.

Another way of designing the partition wall is described in U.S. Pat.No. 1,172,505 wherein an oscillating yoke having two surfaces of contactthat abut against a rotary piston forms the partition wall between thepressure and suction sides in a rotary piston engine that operates as apump. The oscillating yoke and the rotary piston is configured to ensurethat irrespective of the angle assumed by the rotor the yoke will abutagainst the rotor by means of two surface of contact. In addition, theyoke is mounted on a shaft that is attached to the pump housing in afixed point of attachment about which point the yoke pivots.

A necessary prerequisite for this construction is that the sum of thedistance from the centre of the rotary piston to one of the yoke tipsand the distance from the centre of the rotary piston to the other yoketip remains constant at all times. In practice, this means that thesealing force provided by the sealing yoke is directed diametricallyagainst the rotor. A drawback of this design is the restriction that theabove-mentioned condition imposes on the geometry of the rotary piston.Another disadvantage is that the sealing yoke is mounted on a shaft orsimilar means, which adds to the number of components that are exposedto wear and contribute to wedging of particles. A third disadvantage isthat the yoke has large surface areas that are exposed to the medium onthe pressure as well as one the suction sides, for which reason theoutput pressure acting on the rotary piston at the surfaces of abutmentof the yoke increases rapidly at the counter-pressure rises and thenegative pressure increases. Negative pressure on the suction side andexcess pressure on the pressure side cooperate to increasing thepressure of abutment of the yoke on the pressure side. In addition,another consequence of this design is that a large proportion of thepump housing volume becomes inactive and does not take part in thepressure build-up by the rotary piston, in the fluid sealing, and so on.

Patent Specification U.S. Pat. No. 4,047,857 describes anotherconstructional solution for sealing the rotary piston engine. Thisconstruction comprises at least one flexible curved membrane which issecured in a rotor rotating about a stator located interiorly thereof.The sealing membrane consists of a cylindrical stationary bearingportion which is fitted in the rotor to which the membrane is securedand around which the membrane oscillates in operation. The curvedmembrane abuts against the surface of the stator and is adapted to pivotinto a curved recess in the rotor.

Quite apart from the technically complex manufacturing method, thisconstruction, like the previous one, is formed with large pressuresurfaces with resulting high pressure of abutment upon risingcounter-pressures on the outlet side, and the negative pressure on thesuction side co-operates with the excess pressure on the pressure sideto further increase the pressure of abutment of the membrane against thesurface of the stator during the rotation. In addition, the structure isextremely sensitive to the presence of particles that may easily wedgethemselves in the gap formed between the upper face of the membrane andthe recess in the rotor.

A feature common to all prior-art rotary piston engines operating on theprinciple of employing a sealing means in the shape of a yoke or aresilient membrane is that the yoke or the membrane pivots about a fixedcentre line at a predetermined distance from the axis of rotation of therotary piston or the rotary body.

OBJECT OF THE INVENTION

One object of the present invention is to enhance the usefulness ofrotary piston engines in their capacity as all-purpose pumps that lendthemselves to an extended range of applications, which is desirableconsidering the simple mode of operation of this type of engine, byremoving the fundamental drawbacks and weaknesses inherent in thedesigns based on the above outlined structural principles, which isachieved by using a different technical structure for the partition wallthat separates the pressure and suction sides of the pump from oneanother.

This object is achieved in a rotary piston engine of the kind defined inthe appended claims.

SUMMARY OF THE INVENTION

The present invention is distinguished from prior-art rotary pistonengines in that the rotary piston engine in accordance with theinvention is fitted with a sealing element which is movably associatedwith the housing in such a manner that the sealing element isdisplaceable radially, thus allowing the sum of the distances from theaxis of rotation of the rotary body to the points of abutment on saidbody to vary. Among other things, this arrangement makes the rotarypiston engine flexible as regards the configuration of the rotary body,also with respect to wear thereon.

In accordance with another aspect of the invention the sealing elementis displaceable also in and oppositely to the direction of rotation.This feature increases the flexibility and the simplicity of thestructure further. More particularly, it becomes possible to make use ofthe forces exerted in the direction of rotation in order to transformthese forces into radially exerted forces. This may be achieved forexample by forming the intermediated web portion of the sealing elementwith surfaces that are inclined in the direction oppositely to thedirection of rotation, which inclined surfaces are intended to engageportions of the housing in order to transform a force in the directionof rotation to a force in the radial direction. One advantageousembodiment of the rotary piston engine includes holders secured to thehousing and projecting from the internal face thereof, said holdersadapted to co-operate with V-shaped grooves formed in the web portion ofthe sealing elements in order to thus hold said elements in position.

In accordance with yet another aspect of the invention the holders areresiliently secured to the housing in order to be allowed radialdisplacement. In this manner the sealing element exerts its sealingeffect also in the case of low engine speeds or when the engine is notin running.

Further advantages and characteristics of the construction in accordancewith the invention will become apparent from the following descriptionof preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a plan view of one embodiment of a rotary piston engine inaccordance with the invention;

FIG. 2 is a lateral view of the engine of FIG. 1;

FIG. 3 is a longitudinal sectional view on line III—III of FIG. 2;

FIG. 4 is a cross-sectional view taken on line IV—IV of FIG. 1;

FIGS. 5A-5F are views showing the changes of position of the sealingelement upon rotation of the rotary piston of the embodiment of theengine illustrated in FIGS. 1-4;

FIG. 6 shows an embodiment of the engine having several inlet and outletopenings formed in a pump housing, and several sealing elements; and

FIGS. 7A and 7B show alternative embodiments of sealing elements andfastener arrangements.

DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the invention will now be described in the following inmore detail for exemplifying purposes and with reference to theaccompanying drawings.

FIGS. 1-3 illustrate a rotary piston engine in accordance with a firstembodiment of the invention. A housing 1 encloses a rotary body 2mounted on a shaft 3. The housing 1 is provided with inlet and outletopenings 4 and 5. A sealing element 7 is located intermediate the inletopening and the outlet opening and comes upon rotation of the rotarypiston inside the space where sealing element movements are restrictedby a holder 6, the rotary body 2 and two end walls 8 and 9 provided onthe housing 1. The shaft 3 is supported in one or both end walls 8 and 9by means of bearing members 10 and 11, and sealing elements 12 and 13,sealing in the axial direction, are located between the bearing membersand the rotary body. Optionally, also sealing elements 14 and 15,sealing in the radial direction, may be provided in the end walls 8 and9. The end walls and the housing are interconnected by means of screwjoints 21, and sealing elements 19 and 20 are provided on both sides ofthe housing 1 in order to prevent leakage from the engine.

The sealing element 7 may be configured in several different ways but inaccordance with one embodiment shown in FIG. 4, it is designed as aU-shaped means having two leg portions 16 and 17 in abutment against therotary body 2 and presenting, on its face opposite the leg portions, aV-shaped groove 18 widening in the direction away from the two legportions. The length of the sealing element is equal to that of therotary body 2 and the element moves with a light-running fit between thehousing end walls 8 and 9. The height of the sealing element is chosento ensure stability of the element while in motion. The position of theV-shaped groove 18 relative to the two leg portions may be chosen atliberty but preferably the groove is positioned half-way between the legportions. Should an especially low or high abutment pressure be requiredfrom the sealing element, the position of the V-shaped groove is changedin a direction towards or away from, respectively, the leg portionclosest to the outlet opening of the engine, in the case when the latterfunctions as a pump, and in the opposite direction for engine functions.

The housing 1 is formed with a recess from which the inlet and outletopenings depart. The holder 6 is placed intermediate the openings andserves to delimit and to guide the movements of the sealing element 7 inthe rotational plane (co-ordinate directions x and y, the movement inthe direction of the z-co-ordinate being restricted by the end walls 8and 9) during the progress of the rotational movement. Preferably, theholder 6 is formed with an angled tip of lesser angle that the openV-shaped groove 18 formed in the sealing element, the tip being shapedto ensure that the sealing element may pivot freely inside the grooveduring the rotation of the rotary piston.

The rotor 2 is formed by a rotary body which is centrally located insidethe housing 1, being supported therein in bearing means in at least oneof the end wall plates 8 and 9. The cross section of the rotary bodypreferably is uniform along the entire length of the body and it shouldcontain at least one line where the diameter essentially equals thediameter of the housing 1, whereby, upon rotation, at least two chambersare defined between the rotor 2, the housing 1 and the sealingelement(s) 7. In accordance with the embodiment illustrated in thedrawing figures, the rotary body is shown as a regular polygon,manufactured from a cylinder from which material has been milled away toform the faces of the polygon, FIG. 4 shows a rotary body having eightequal sides.

During the rotation of a polygon body the sum of the distances from twoarbitrarily chosen points of contact of the leg portions 16 and 17 atthe periphery of the body is not constant but the sum of the distancevalues changes depending on the angular position of the body. For thisreason it is necessary that a sealing element which is to seal against arotary body of this kind be able to move in the plane of rotation duringthe rotation while at the same time being able to perform its sealingaction to ensure that a counter-pressure is maintained.

The engine in accordance with the invention operates in the followingmanner. During the rotation of the rotary body 2 in the directionindicated by an arrow opening 4 is the inlet opening and opening 5 theoutlet opening when the engine operates as a pump. Fluid enters throughopening 4 and fills the inlet chamber A defined between means 1, 2, 6,7, 8, and 9. Upon its rotation, the rotary piston carries along fluidpresent in the spaces B₁-B₅ defined between the flat sides of the rotarypiston and the wall of the pump housing, thus causing a negativepressure to generate in A and more fluid to be sucked in through theopening 4. The fluid is carried to the outlet chamber C. The means 6 and7 block the transport between A and C, the fluid thus being forced toexit through the outlet opening 5. During the rotation, means 7 takespart in the movements of the rotary piston, said movements beingcontrolled by the two-face abutment of the leg portions 16 and 17against the rotor and by a force urging the means 7 against the rotor.This force consists of the radially directed component of the totalforce that is being built up by the pressure of the fluid in the outerchamber, the negative pressure in the inlet chamber and the frictionarising between means 7 and the rotor 2 during the rotation and that istransferred through a wedging effect as the means 7 abuts against theholder 6.

FIG. 5 illustrates the manner of movement of the sealing element duringthe rotation, FIGS. 5A-F showing sequentially the rotation of the rotor2. FIG. 5B shows the position of the means 7 relative to the rotor 2when the sum of the distances a1+a2 from the leg portions to the centreof the rotor axis is at its maximum. In this position the sealingelement 7 is furthest away from the centre of the axis of rotation 3 andconsequently, in this position, the tip of the holder 6 assumes itslowermost position inside the groove 18 of the sealing element.

Upon continued rotation of the pivot shaft/axis of rotation the positionillustrated in FIG. 5C is reached, in which position the distances fromthe leg portions 16 and 17 to the axis centre are b1 and b2,respectively. The sum of b1 and b2 is smaller than the sum of a1 and a2,and consequently the means 7 is closer to the centre of rotation of therotary piston, with the result that the tip of the holder 6 now isfurther away from the bottom of the groove 18 and that in addition thepoint of engagement between means 6 and 7 is displaced further away fromthe centre line of groove 18 than is the case in FIG. 5B.

Upon further rotation of the rotary body to the position illustrated inFIG. 5E, the means 7, in accordance with the shown embodiment, hasreached its position closest to the centre axis, i.e. the sum ofdistances c1 and c2 from the axis centre to the leg portions 16 and 17is smaller than the sum a1+a2 and b1+b2, respectively. In this case,means 7 has moved closer to the centre of the axis of rotation andtherefore the distance from the bottom of the V-shaped groove 18 to thetip of the holder 6 is at its maximum, with the added consequence thatalso the displacement between the point of engagement of means 6 and 7relative to the centre line of the V-shaped groove 18 is at its maximum.

Upon further rotation of the rotary piston, means 7 is returned to itsmaximum position, i.e. the tip of the holder 6 is carried downwardsinside the groove 18 and the means 7 increases its distance from theaxis of rotation.

The principle of sealing-element movements is applicable to all types ofgeometrical profile configurations that may be used for the rotarypiston.

It is essential for the function of the rotary piston engine inaccordance with the invention that the position of the sealing elementis constantly defined by the rotary piston acting on the leg portions ofthat element and that a radial force acts on the sealing element duringoperation to ensure abutment of the leg portions against the rotarybody. To achieve this, a pivotal movement about an axis of rotation onthe sealing element is required, and this axis of rotation migrates onthe sealing element when arbitrary rotary bodies are used and when theelement at the axis of rotation pivots against a fixed back-up means 6.In consequence of the migration of the axis of rotation, during therotation, the sealing element will be displaced forward and backwards inparallel with the housing, i.e. in or oppositely to the direction ofrotation, and therefore it will be displaced also radially, i.e. thedistance from the axis of rotation to the plane containing the points ofabutment is allowed to vary.

A rotary piston engine conceived in this manner possesses severaladvantages compared with already known constructions, among them that:

1. The construction affords considerable freedom of choice andflexibility as regards the design of the geometrical configuration ofthe rotor.

2. The sealing element is self-adjusting for adaptation to the gradualwear on the rotor and the sealing element.

3. The construction makes possible a simple structure of the rotarypiston engine.

4. Only a limited part of the pump housing is used for accommodating thesealing element compared with the principles on which are based theconstructions including a yoke the sealing action of which is exertedagainst two diametrically opposite points on the rotary piston. Theembodiment according to which the engine is used as a pump offersconsiderable advantages, since an extremely high suction capacity isobtained as a result of the existence of several sealing surfacesbetween sectors B1-B5. The principle of construction on which theinvention is based also allows several inlet and outlet openings to beprovided around the periphery of the housing, with resultingconsiderable increase of capacity while at the same time a practicallyconstant flow may be obtained.

5. Because the sealing element pivots constantly while moving radiallyand along the periphery of the rotor, the joint becomes self-cleansing.

6. The engine may run under no-load conditions for a prolonged period oftime without there being any risk that detrimental frictional heatgenerates between the sealing element and the rotor since when no loadis on the engine no fluid pressure builds up on the pressure or suctionside and consequently the pressure of abutment between the sealingelement and the rotary piston is close to zero. In practice, this is ofutmost importance as it minimizes risks of engine breakdown during dryengine running conditions.

7. The construction offers large freedom of choice of materials fordifferent applications of the engine and to achieve special operationaltechnical advantages from the rotary piston engine. For example, thepump may be manufactured from PE and PP plastics when used in thechemico-technical industry. Another example is to choose a rotary pistonof acetal plastics and a sealing element made from stainless steel, orvice versa, thus further enhancing the excellent properties during thedry engine running conditions referred to in point 6 above.

8. The sealing element may be modified to satisfy particular needs; forexample a return flow may be made to pass through the element to providepressure relief and lubrication.

It is of course possible to use several pairs of respectively inlet andoutlet openings in one and the same rotary piston engine, with sealingelements being positioned intermediate the openings, in order toincrease the engine performance. For example, in FIG. 6 is shown onemodified embodiment using three sealing elements.

FIG. 7A illustrates yet another embodiment wherein the radial movement,i.e. the distance from the sealing element pivot axis to the rotary bodycentre axis, is adjusted by a spring-loaded displaceable holder.Optionally, the sealing element pivot axis may in this case be fixedrelative to the securement means. In accordance with this embodiment ofthe sealing element and the holder, the sealing element 7 abuts againstthe rotary piston also when no pressure differential exists between theinlet and outlet chambers A and C, because the holder is exposed tospring action and in consequence thereof urges the sealing elementradially downwards, against the rotor 2.

FIG. 7B illustrates a further alternative embodiment of the sealingelement. In accordance with this version there is no separate holder.Instead, an upwardly protruding member including downwardly slopingfaces is formed on the web portion intermediate the two leg portions ofthe sealing element. These sloping faces are adapted to cooperate withedges formed in a recess in the internal wall of the housing. In thismanner a wedging effect similar to that found in the initially describedembodiment of the invention is obtained, for transforming a force actingin the direction of rotation to a force acting in the radial direction.

It goes without saying that further modifications of the invention arepossible. Such obvious modifications must be considered to be within thescope of protection of the invention as the latter is defined in theappended claims.

What is claimed is:
 1. A rotary piston engine to be used as a pump or aengine, comprising: a housing fitted with end walls; a rotary bodyrotatably mounted in said housing; and at least one sealing elementseparating a volume formed between the housing and the rotary body, saidhousing having at least one pair of inlet and outlet openings and thesealing element having two leg portions, the ends of which abut againstthe rotary body, and a web portion intermediate said leg portions, saidsealing element additionally being pivotable about a pivot axis on saidweb portion, wherein said sealing element is movably associated with thehousing in such a manner that the sealing element is displaceableradially, thus allowing the sum of the distances from the axis ofrotation of the rotary body to the points of abutment on said body tovary, said sealing element is also displaceable in and oppositely to thedirection of rotation, and the intermediate web portion of the sealingelement is formed with surfaces that are inclined in the directionoppositely to the direction of rotation, which inclined surfaces areintended to engage portions of the housing in order to transform a forcein the direction of rotation to a force in the radial direction.
 2. Arotary piston engine as claimed in claim 1, further comprising holderssecured to the housing and projecting from the internal face thereof,said holders adapted to co-operate with V-shaped grooves formed in theweb portion of the sealing elements in order to thus hold said elementsin position.
 3. A rotary engine piston as claimed in claim 2, whereinsaid holders are resiliently secured to the housing in order to beallowed radial displacement.